The present invention relates generally to a device and method for monitoring fluids and, in particular, to a device and method for determining the quality, intensity and/or level of a fluid by evaluating the shape of a polarized beam of light.
Electromagnetic radiation (e.g., ultraviolet, visible or infrared light) can be used to non-destructively characterize the chemical composition of gases, fluids and solids through absorption or scattering. "Optical absorption" involves the conversion of energy from the electromagnetic field into excitation of the electron energy levels of the elemental atoms or compounds present. "Light scattering" refers to the redirection of part of the light beam along paths different from that of the original beam (e.g., Rayleigh, Rayleigh-Brillouin and Mie scattering).
In the context of the present invention, the term fluid "intensity" refers to the degree of or magnitude of contamination resulting from the presence of foreign particles and/or liquid dispersions in the fluid. By contrast, the term fluid "quality" refers to the degree of degradation as a result of fluid usage. The term fluid "parameter" refers broadly to one or more variables associated with the fluid, such as intensity, quality and/or level.
With respect to lubricating oils and many other fluids, increased contamination or degradation of the fluid will result in increased absorption and scattering. Therefore, if a beam of light is transmitted through fresh oil, the shape of the transmitted beam will be isotropic. However, if the same beam of light is transmitted through either degraded oil or contaminated oil, the shape of the transmitted beam will be anisotropic. In fact, the shape of the transmitted beam becomes more anisotropic as the contamination and/or degradation increases. Thus, the intensity and the quality of the fluid may be determined by evaluating the shape of the transmitted beam.
There are a number of known applications for fluid monitors. For example, the operator of an automobile periodically monitors oil quality and level or risks costly damage to the engine. The degradation of engine oil in passenger automobiles and trucks depends on factors such as the initial oil quality, engine type, engine condition, engine load, oil operating temperature, usage time, length and distance of driving, oil consumption and individual driving habits. A general guideline for oil change intervals suitable for all drivers is difficult to establish.
One prior art device for monitoring the oil level in an automobile engine is a dipstick. A conventional dipstick does not measure oil quality or intensity, and it must be manually removed to determine the level of the oil. While electronic dipsticks are now available which allow drivers to monitor the oil level without physically removing the dipstick, electronic dipsticks do not measure oil quality or intensity.
An optical oil monitor is disclosed in U.S. Pat. No. 3,876,307 to Skala. This monitor (i) measures degradation in oil by passing light through an oil sample and picking up the light that is scattered at 90 degrees by the molecules and particles and (ii) measures chemical breakdown by the attenuation of the light passing substantially straight through the oil. It has been found that measuring degradation in oil based on the amount of light scattered at 90 degrees is not reliable because the highest level of degradation that the monitor can detect is still below the degradation level at which the oil should be replaced. In other words, the monitor becomes ineffective well before the oil must be replaced.
Another known oil level monitor, which is described in U.S. Pat. No. 5,021,665 to Ames, determines the fluid level in a reservoir by evaluating the intensity of fluorescent radiation emitted by the fluid. While this device adequately monitors the oil level, it is not acceptable for determining oil quality in an automobile. As with the Skala monitor, it has been found that the oil quality may still be acceptable for some time after the oil has absorbed the radiation to the point that no more radiation can be detected by the monitor.
Other existing methods for measuring oil quality and intensity are not practical for applications such as the operation of an automobile. Such methods would require the automobile operator to periodically remove a sample of the oil and transport it to a location equipped for testing the oil quality and intensity. Such methods are inefficient from both a time and a cost standpoint and are not capable of evaluating the fluid in situ.
Accordingly, there exists a need for a practical and cost-effective means for monitoring the quality of a fluid to eliminate unnecessary maintenance and to reduce costly repairs resulting from the use of degraded fluid. There is also a need for a practical and cost-effective means for monitoring the intensity of a fluid to detect the presence of contaminants as soon as possible so that the source of the contamination can be identified. Further, there is a need for a fluid level monitor which is also capable of effectively monitoring the quality and/or intensity of a fluid.